The Idle Air Control Valve (IACV) is a digital linear actuator (DLA) which accurately controls throttle airflow in an engine system. The need for using an IACV is that vehicle pollution emission control regulations require more precise air/fuel ratios and thus cleaner tailpipe emissions. The IACV is an automotive grade can-stack style stepper motor.
The vehicle environment, for which the IACV is used, can be extreme from the cold temperatures of the artic, to hot dusty deserts, to rain soaked jungles. Under normal vehicle driving conditions, the automotive intake manifold air filtration system is sufficient to protect the IACV from contamination. In the extreme vehicle applications, the IACV can be exposed to the following contamination; dust, moisture, fuel, EGR hot gas, carburetor cleaners, etc. The presence of contaminates in the IACV can lead to reduced component life and subsequent customer complaints or warranty returns.
Currently, there are two components which can be used as barriers to reduce the contamination exposure of the IACV; the grime shield or cover bellows. A grime shield is a metallic cylinder which shrouds a grease covered shaft of the IACV. It can reduce particulate contact with the shaft grease, but is not a barrier that can exclude contaminants. With regard to bellows, there are two styles that are used in current production to reduce the contamination exposure of the IACV. A first type of bellows is used with an IACV in manifold applications and a second type of bellows is used in non-manifold DLA applications for environmental splash protection. Both types of bellows are effective but have shortcomings.
The first type of bellows can be assembled into an IACV. The geometry and rubber material chosen is typically such that the bellows retains its dimensions when exposed to manifold vacuum. One end of the bellows has a press fit insertion into a housing nose. The opposite end of the bellows fits over a skirted cap-nut or pintle, which then requires two O-rings as a radial compression. This is not a proper use of an O-ring. Besides the manufacturing difficulties of stretching the O-ring over the cap nut diameter, the O-ring has potential to tear or crack. Over time, the O-ring could then harden or eventually break-off allowing the bellows to detach from the cap nut. In addition, secondary radial retention components such as springs or clips are required to secure the cap-nut to the bellows.
The second type of bellows can be assembled into a DLA. The geometry and rubber material chosen for this type of bellows serves as a hermetic barrier. Exposing the bellows to manifold vacuum will invert the bellows and thus change it dimensionally. Because of the soft rubber material, one end of the bellows must be glued to a housing nose. This assembly process is difficult and a messy operation.
There is a need to provide an improved bellows for an IACV.